| Czochralski (CZ) silicon is the fundamental material for integrated circuits (ICs). This is essentially due to that CZ silicon contains oxygen impurity which is inevitably incorporated during the crystal growth. On one hand, the oxygen impurity increases the mechanical strength of silicon crystal; on the other hand, oxygen impurity atoms will be aggregated into oxygen precipitates and furthermore induce secondary defects, which can exert gettering effect on the detrimental metal contamination during the fabrication of ICs. In this context, oxygen precipitation (OP) in CZ silicon has been an everlasting subject of significance. Oxygen diffusion is a kinetic condition for OP in CZ silicon. Therefore, understanding oxygen diffusion in CZ silicon is essential for studying OP. With the great research efforts in the past several decades, the behaviors of oxygen diffusion and OP in lightly doped CZ silicon have been gained insight. By comparison, the effects of heavy doping of dopants and co-doping of electrically inactive impurities on the oxygen diffusion and OP in CZ silicon have not been substantially understood. In this dissertation, experiments and first-principles calculations are combined to study the impacts of heavy phosphorus (P)-, boron (B)-doping and tin (Sn)-codoping on oxygen diffusion and OP in CZ silicon. Besides, the influence of interactions between B and point defects on the electrical properties of heavily B-doped silicon has been investigated. The achieved results are beneficial for understanding the interactions of impurities, oxygen and point defects as well as their impacts on oxygen diffusion and OP in CZ silicon. Listed below are the primary achievements in this dissertation.(1) The impact of Sn doping on interstitial oxygen (Oi) diffusion is investigated by first-principles calculations. It is found that the oxygen diffusion energy barrier increases with the expanded lattices caused by the Sn doping. Structure analysis indicates that the geometric parameters of the angle of Si-O-Si and the bond length of Si-O increase with the lattice expansion, drawing the Oi atom back towards the Si-Si bond center, leading to an increased energy barrier for an Oi atom to jump between the neighboring Si-Si bond interstitials. Besides, SnV pair can act as Oi atom traps, resulting in the formation of SnVO complex with a binding energy of～2.26eV. It is predicted from the calculations that OD in heavily Sn-doped CZ silicon will be retarded.(2) The effect of heavy B doping (～3×1019cm-3) on oxygen diffusion has been experimentally and theoretically investigated. It is found that the retarding effect of heavy B-doping on oxygen diffusion is temperature dependent. The oxygen out-diffusion profiles can only be fitted by two independent error functions, from which two values of activation energies for oxygen diffusion are derived:one is2.40±0.05eV, close to the conventional value in lightly B-doped CZ silicon, the other is much larger, being3.80±0.16eV. First-principles calculations suggest that the ring-like Bi-Oi pair can exist in the-Bi-Si-Oi-Si-Bi-configuration. The Bi-Oi pair can diffuse coordinately in the silicon lattice, which may account for the possible new oxygen diffusion mechanism.(3) The impact of heavy P-doping on oxygen diffusion and the underlying mechanism is theoretically investigated. It is found that the P atom can act as trap center of Oi atoms, introducing12equivalent trap sites at its second nearest neighboring Si-Si bond centers, leading to the formation of P-O pairs in the-P-Si-O-Si-configuration. Furthermore, the calculated increase in the oxygen diffusion activation energy taking account of the trapping effect of such P-O pairs is-0.04-0.07eV, which is in accordance with the experimental values. This indicates that the retarded oxygen diffusion can be ascribed to the trapping of Oi atoms associated with the formation of the P-O pairs.(4) The effect of Sn codoping on point defects and OP in CZ silicon is investigated. It is found that Sn plays different roles in affecting OP according to the amount of vacancies:Sn suppresses OP in vacancy-lean CZ silicon but promotes OP in vacancy-rich silicon. The effects of Sn-doping on the formation and annihilation of point defects as well as on the evolution of vacancy-a nd oxygen-related complexes have been systematically studied using first-principles calculations. Based on the experimental and theoretical results, it is postulated that Sn atoms in silicon act as vacancy reservoirs which modify the formation and annihilation of vacancies as well as the evolution of vacancy-related complexes. The mechanism for the different roles of Sn in affecting OP is discussed based on the calculation results.(5) OP in heavily B-doped CZ silicon has been investigated. Anomalous OP behavior is found in heavily B-doped CZ silicon. That is, oxygen precipitate nuclei can be readily formed by a quite short nucleation time of0.5h at650℃, thus enhancing OP in the subsequent high temperature anneal; while, the extension of650℃anneal is instead not favorable for OP in the subsequent high temperature anneal. Moreover, the pre-anneal at1200℃cannot substantially eliminate the grown-in OP. The oxygen diffusion, oxygen precipitate size and morphology have been investigated. Combining with the first-principles calculations, a tentative model for OP in heavily B-doped CZ silicon has been proposed.(6) The changes in hole concentration of heavily B-doped CZ silicon subjected to rapid thermal processing (RTP) and following conventional furnace anneal (CFA) have been investigated. It is found that decrease in hole concentration, namely, B deactivation is observed starting from1050℃and increases with RTP temperature. The following CFA at300-500℃leads to further B deactivation, while that at600-800℃results in B reactivation. First-principles calculations suggest that the interaction between B atoms and silicon self-interstitials (I) thus forming BI pairs leads to the B deactivation during the RTP, the formation of extended B2I complexes overcoming an energy barrier of0.39eV results in further B deactivation in the following CFA at300-500℃. On the contrary, the dissociation of BI and B2I pairs which require activation energies of～1.08eV and0.95eV during the following CFA at600-800℃enables the B reactivation. |
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